The present invention relates to a novel and efficient method for culturing a basidiomycetous fungus in an aqueous liquid culture medium or, more particularly, to a method for culturing an edible basidiomycetous fungus such as Mushroom Agaricus Blazei Murill, Cortinellus shuitake, Lyophyllum aggregatum, Pleurotus ostreatus and the like in an aqueous liquid culture medium to obtain aggregates of the fungus body having a several centimeter size as well as to a bioreactor for practicing the culturing method.
Methods for culturing a basidiomycetous fungus in a liquid culture medium are known as disclosed, for example, in U.S. Pat. Nos. 2,693,665, 2,761,246 and 2,850,841 and elsewhere. A typical liquid culture medium used in the prior art contains 50 g of sucrose, 10 g of ammonium nitrate, 5 g of sodium phosphate, 2.5 g of magnesium sulfate and 0.2 g of iron (II) sulfate each per liter of the liquid culture medium. The liquid culture medium inoculated with the fungus body such as mycelia is gently agitated with a stirrer rotating at a relatively low revolution in air for several days to effect growth of the mycelia into aggregates of globular or polyhedral granules having a diameter of 3 to 40 mm. It is accepted that such an aggregate of mycelia is formed by virtue of the viscous polysaccharide material formed on the surface of the mycelium to act like an adhesive. The productivity of these prior art methods, however, is very low due to the low growth rate of the fungus and a difficulty encountered in the recovery of the fungus body as grown from the culture medium.
The present invention accordingly has an object to provide a novel and efficient industrial method for culturing a basidiomycetous fungus such as Mushroom Agaricus Blazei Murill, referred to as Agaricus fungus hereinafter, and the like in a liquid culture medium. A secondary object of the invention is to provide a novel bioreactor suitable for practicing the above mentioned culturing method in a liquid culture medium for the fungus.
Thus, the method of the present invention for culturing a basidiomycetous fungus in an aqueous liquid culture medium comprises the steps of:
(a) inoculating a liquid culture medium containing inorganic nutrient salts for nitrogen, phosphate and potassium with a body of the fungus such as mycelia;
(b) admixing the liquid culture medium with crude cane sugar in an amount in the range from 50 g to 70 g calculated as sucrose per liter of the liquid culture medium;
(c) admixing the liquid culture medium with a water-insoluble growth-supporting material selected from the group consisting of crushed sugarcane, sugarcane bagasse and wheat bran in an amount in the range from 0.2 g to 15 g as dry per liter of the liquid culture medium;
(d) keeping the liquid culture medium under agitation at a temperature in the range from 20 to 30 xc2x0 C.; and
(e) blowing, into the liquid culture medium, oxygen-enriched air containing at least 30% by volume or, preferably, from 60 to 90% by volume of oxygen under a pressure in the range from 0.12 to 0.5 MPa (absolute) at a rate of at least 0.01 liter/minute per liter of the liquid culture medium.
The bioreactor for practicing the above described inventive culturing method comprises:
(A) a pressurizable vessel for containing a liquid culture medium;
(B) a gas inlet tube capable of blowing oxygen-enriched air into the liquid culture medium under a superatmospheric pressure in the range from 0.12 to 0.5 MPa (absolute);
(C) gas outlet tube having a means for regulating the pressure inside of the pressurizable vessel at a pressure in the range from 0.12 to 0.5 MPa (absolute); and
(D) a means for agitating the liquid culture medium contained in the pressurizable vessel.